The disclosure of Japanese Patent Application No. 2002-253999 filed on Aug. 30, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to control apparatus and method for a variable valve actuating system of an internal combustion engine.
2. Description of Related Art
For example, U.S. Pat. No. 6,401,675 B1 discloses a valve actuating system for lifting intake valves of an internal combustion engine, which system is provided with a lift characteristic changing mechanism for changing lift characteristics of the intake valves. The lift characteristic changing mechanism disclosed in the above-identified U.S. Patent is arranged to be driven by an electric motor.
In the valve actuating system as described above, characteristics or tendencies of changes in the lift characteristics of the intake valves effected by the lift characteristic changing mechanism change depending upon output characteristics of the electric motor, and the output characteristics of the electric motor change depending upon the environment surrounding the electric motor. For example, the output torque of the electric motor changes depending upon the temperature of the electric motor, more specifically, the output torque of the electric motor decreases as the temperature of the electric motor rises. Where the output torque of the electric motor is reduced, the lift characteristics of the intake valves may not be changed as desired even if the lift characteristic changing mechanism is driven by the electric motor.
The above-described problem occurs not only to the valve actuating system provided with the lift characteristic changing mechanism for changing the lift characteristics of the intake valves, but also to a valve actuating system for lifting exhaust valves of the engine, which system is provided with a lift characteristic changing mechanism for changing lift characteristics of the exhaust valves.
It is therefore an object of the invention to provide control apparatus and method for controlling a valve actuating system for changing lift characteristics of intake valves or exhaust valves of an internal combustion engine as desired.
To accomplish the above and/or other object(s), there is provided according to the invention a control apparatus for a valve actuating system which is operable to lift an intake valve or an exhaust valve of an internal combustion engine and includes a lift characteristic changing mechanism for changing a lift characteristic of the intake valve or the exhaust valve, comprising a controller that calculates a target operation value of the lift characteristic changing mechanism, calculates a realizable range of the operation value which can be realized by the lift characteristic changing mechanism, based on a controlled variable that can be given to the lift characteristic changing mechanism and at least one parameter related to an environment surrounding the lift characteristic changing mechanism, and calculates a new target operation value to be within the realizable range of the operation value when the target operation value is not within the realizable range of the operation value. Here, the lift characteristic changing mechanism may be in the form of a lift amount changing mechanism or a lift timing changing mechanism as described later.
When the target operation value of the lift characteristic changing mechanism is within the realizable range of the operation value, the control apparatus controls the lift characteristic changing mechanism according to the target operation value. When the target operation value of the lift characteristic changing mechanism is not within the realizable range of the operation value, on the other hand, the control apparatus determines a new target operation value within the realizable range, and controls the lift characteristic changing mechanism according to the new target operation value. Accordingly, the lift characteristic of the intake valve or the exhaust valve of the engine can be made equal to a target value.